Method for plasma etching performance enhancement

ABSTRACT

A method for etching a feature in a layer through an etching mask is provided. A protective layer is formed on exposed surfaces of the etching mask and vertical sidewalls of the feature with a passivation gas mixture. The feature is etched through the etching mask with reactive etching mixtures containing at least one etching chemical and at least one passivation chemical.

RELATED APPLICATIONS

This application claims priority under 35 USC 119(e) from theProvisional Application No. 60/417,806 entitled “IN-SITU PLASMA VAPORDEPOSITION AND ETCH METHOD FOR PLASMA ETCH PERFORMANCE ENHANCEMENT,”which was filed on Oct. 11, 2002, hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method of obtaining a structure on asemiconductor wafer by etching through structures defined by an etchmask using a plasma.

2. Description of the Related Art

In semiconductor plasma etching applications, a plasma etcher is usuallyused to transfer a photoresist mask pattern into a circuit and linepattern of a desired thin film and/or filmstack (conductors ordielectric insulators) on a Si wafer. This is achieved by etching awaythe films (and filmstacks) underneath the photoresist materials in theopened areas of the mask pattern. This etching reaction is initiated bythe chemically active species and electrically charged particles (ions)generated by exciting an electric discharge in a reactant mixturecontained in a vacuum enclosure also referred to as a reactor chamber.Additionally, the ions are also accelerated towards the wafer materialsthrough an electric field created between the gas mixture and the wafermaterials, generating a directional removal of the etching materialsalong the direction of the ion trajectory in a manner referred to asanisotropic etching. At the finish of the etching sequence, the maskingmaterials are removed by stripping it away, leaving in its place replicaof the lateral pattern of the original intended mask patterns. Thisetching method is illustrated in FIGS. 1A-C. In this method, a plasmaetching process is used to transfer directly the photoresist maskpattern 104 into that of the underlying oxide dielectric thin film 108,as shown in FIG. 1A. The etching generates a contact hole 112 and erodesand damages the, photoresist 104, as shown in FIG. 1B. The photoresistis then removed leaving the contact hole 112 in the oxide 108, as shownin FIG. 1C. During the etching process, the mask materials are usuallyeroded and/or damaged in exchange for the pattern transfer.Consequently, some of the damage and erosion also may be transferred tothe underlying layers leaving such undesirable pattern distortions suchas striation, CD enlargement, etc.

The objective of the etching methodology, therefore, includes reducingthe photoresist mask erosion to enhance the fidelity of the patterntransfer from the photoresist mask patterns. For this purpose, it hasbeen proposed to include a passivation gas in the reactive etchingmixture. This passivation gas can be chosen in such a way that itspresence selectively reduces the etching damage and erosion of themasking materials relative to the removal rate of the thin filmmaterials to be etched. The passivation gas can be chosen in such a waythat, an etching retardation coating is generated on the surface of themasking materials acting as a barrier to slow down the etching reaction.By design, the passivation gas is chosen in a way that it additionallybeneficially forms an etching retardation coating on vertical surfacesof the film structures to be etched, such that etching reaction can notadvance in the absence of the ion bombardment. By the nature of thevertical trajectory of the charged particles, etching can thereforeadvance only in the vertical direction, with little to no etching in thelateral direction, creating an anisotropic etching profile. Hence, thepresence of a passivation gas in the etching mixture is very importantfor the advantage of better etching mask protection and highlyanisotropic etching profile by the use of relatively high energydirectional ion bombardment.

It has already been proposed that the reactive gas mixture containetching gases and polymer formers, with the latter acting the role of apassivation gas. In this case, the etching gases release highly reactivespecies by the excitation of an electrical discharge, which in turnetches the thin film materials to be etched as well as the maskingmaterials by the mechanism of a spontaneous reaction. By the nature ofspontaneous reactions, the etching reaction advances in both thevertical as well as the lateral surfaces, creating isotropic etchingprofiles. The co-presence of a polymer former, through generation of apolymer deposit on the surface of the etching structures and maskingmaterials, can be used to create simultaneously high etching selectivityto masking materials and etching anisotropy, in conjunction with the ionbombardment.

It also has already been proposed that the reactive gas mixture containpolymer former gases and an etching enabler gas. The role of the etchingenabler gas is to enable the polymer former gas to release highlyreactive species by reacting with the polymer former gases in thepresence of an electrical discharge. Alternatively, a retardationcoating on the etching materials as well as the masking materials canalso be formed by chemical reaction of a properly chosen passivation gasdirectly with the surfaces of these materials.

A common disadvantage of the above mentioned methods is that the optimumconditions for different aspects of the etching requirement usually donot coincide and by mixing the gases some of the unique properties ofeach precursor gases may be lost due to inter-reactions. The etchingcondition optimization almost always involve complex trade-offs into asingle etching condition that may not be the optimum should thedifferent etching chemistries be separate.

A variant of the etching methodology is taught in U.S. Pat. No.5,501,893, issued Mar. 26, 1996 to Laermer et al., entitled “Method ofAnisotropically Etching Silicon”. This method separates out the etchinggases and polymer former gases into two different steps, each consistingpurely of one type of chemicals but not the other. This allows for fastetching rate at low ion bombardment energies, since at low ionbombardment energies, high selectivities to masking materials can beachieved for certain spontaneous etching reactions if the activationenergy is slightly lower for the reaction at the surface of the etchingmaterials than the masking materials. By removing the polymer formerfrom the etching process, on the other hand, the etching. process wouldnecessarily be isotropic during the duration when the etching isproceeding, since there is no retardation layer to prevent the lateraletching from occurring. Additionally, without the passivation gas in theetching mixture, it would be difficult to obtain sufficient etchingselectivity to the masking materials if the desire is there to usehigher ion energies. Many etching applications can benefit from high ionbombardment energy to obtain high aspect ratio structures in very smalldimension structures, for example.

Additional proposed methods include a stacked masking scheme to improvethe overall etching resistance of the masking materials. This isillustrated in FIGS. 2A-F. In FIG. 2A an oxide layer 204 is provided.FIG. 2B shows a hardmask layer 208 placed over the oxide layer. Aphotoresist mask 212 is placed over the hardmask layer 208, as shown inFIG. 2C. The photoresist mask 212 is used to pattern the hardmask layer208 to create a patterned hardmask layer 214, and the photoresist layer212 may be removed, as shown in FIG. 2D. A contact hole 216 is etched inthe oxide layer 204, using the patterned hardmask layer 214 as a mask asshown in FIG. 2E. The hardmask is then removed leaving the contact 216in the oxide layer 204, as shown in FIG. 2F.

The advantages of this method are that, by having a more inert hardmaskfrom which to transfer patterns (circuits and lines) to the underlyingfilms, the etch performance is much enhanced and the requirement on theetching and photolithography is also much reduced. The disadvantages ofthis method are that, by introducing new process steps and new tool setsinto the process flow, it is of higher cost and lower overallthroughput. In addition, the extra process complexity also introducesdifficulties by itself. For example, the Si hardmask used for dielectriccontact etch applications is not as easily stripped as the photoresistmask.

The purpose of this invention is to provide a generic method for etchinga feature in a layer or a stack of layers to obtain a high fidelityreplica of a lateral pattern formed by a masking material withsimultaneously high etching anisotropy and high selectivity to themasking materials as well as to the stop layers

SUMMARY OF THE INVENTION

To achieve the foregoing and in accordance with the purpose of thepresent invention, a method for etching a feature in a layer through anetching mask is provided. A protective layer is formed on exposedsurfaces of the etching mask and vertical sidewalls of the feature witha passivation gas mixture. The feature is etched through the etchingmask with reactive etching mixtures containing at least one etchingchemical and at least one passivation chemical.

In another embodiment of the invention, an apparatus for etching a layerunder an etch mask, where the layer is supported by a substrate, isprovided. A plasma processing chamber comprising a chamber wall forminga plasma processing chamber enclosure, a substrate support forsupporting a substrate within the plasma processing chamber enclosure, apressure regulator for regulating the pressure in the plasma processingchamber enclosure, at least one electrode for providing power to theplasma processing chamber enclosure for sustaining a plasma, a gas inletfor providing gas into the plasma processing chamber enclosure, and agas outlet for exhausting gas from the plasma processing chamberenclosure is provided. A deposition gas source and an etchant gas sourceare provided. A first control valve in fluid connection between the gasinlet of the plasma processing chamber and the deposition gas source anda second control valve in fluid connection between the gas inlet of theplasma processing chamber and the etchant gas source are provided. Acontroller controllably connected to the first control valve, the secondcontrol valve, and the at least one electrode comprising at least oneprocessor and computer readable media is provided. The computer readablemedia comprises computer readable code for opening the first controlvalve for at least one deposition step to provide a deposition gas fromthe deposition gas source to the plasma processing chamber enclosure,computer readable code for closing the second control valve for the atleast one deposition step to prevent etching gas from the etching gassource from entering the plasma processing chamber enclosure, computerreadable code for opening the second control valve for at least oneetching step to provide an etching gas from the etching gas source tothe plasma processing chamber, and computer readable code energizing theat least one electrode to provide a bias of greater than 250 volts onthe substrate for at least one etching step.

These and other features of the present invention will be described inmore details below in the detailed description of the invention and inconjunction with the following figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIGS. 1A-C are schematic views of the formation of a contact holefeature through a prior art process.

FIGS. 2A-F are schematic views of the formation of a contact holefeature through another prior art process.

FIG. 3 is a flow chart of an inventive passivation and etch process.

FIGS. 4A-F are schematic views of the formation of a contact hole usingthe inventive process.

FIG. 5 is a schematic view of a system that may be used in practicingthe invention.

FIG. 6 is a micrograph of a plurality of high aspect ratio contact holepatterns formed using the invention.

FIG. 7 is a micrograph of a plurality of high aspect ratio contact holepatterns formed using a prior art process.

FIGS. 8A-B are schematic views of a computer system that may be used inpracticing the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail with reference toa few preferred embodiments thereof as illustrated in the accompanyingdrawings. In the following description, numerous specific details areset forth in order to provide a thorough understanding of the presentinvention. It will be apparent, however, to one skilled in the art, thatthe present invention may be practiced without some or all of thesespecific details. In other instances, well known process steps and/orstructures have not been described in detail in order to notunnecessarily obscure the present invention.

The said invention is a new etching method in which an in-situpassivation process is combined and integrated with an etch process toenhance the overall etch performance without unduly sacrificingsimplicity and cost-effectiveness.

In this new method, an in-situ plasma chemical process is used toenhance and/or repair the photoresist mask, as well as the verticalsidewalls of etching features, during the etching progression. Duringthis new etch sequence, a plasma chemical process step is initiated fora short duration before and/or after the wafer is exposed to an etchingplasma for a desired duration. The plasma passivation process is chosenin such a way that a thin film of material coatings is formed on themask pattern to protect the mask from later etch erosion. Preferably,this thin coating is of a material that is compatible with laterstripping process for ease of final removal but more etch resistant thanthe mask materials. For example, a carbon-rich thin film, containingvery low to no amount of other elements, can be used to coat aphotoresist mask so that protected mask features is noteasily eroded bythe subsequent etching process. In other words, it changes the surfacecomposition of the mask pattern such that the mask behaves like a pseudohardmask, having certain beneficial etching characteristics of anamorphous carbon hardmask. Alternatively, the passivation process mayalso be used in such a way that the formation of the thin coating on themask pattern largely compensates for and/or repairs the mask patternsdamaged/eroded by the prior etch process. The relative inertness of thecoating to the subsequent etching reaction is beneficial so as to not toalter the fine balance obtained in the etching step.

The etching gas mixture contains etchant species and at least onepassivation species so as to not lose the benefits associated with apassivation gas in the etching chemistry. The ratio of the etching topassivation components, along with a plurality of other processingconditions, is finely balanced to achieve optimum processing results,such as photoresist selectivty, etching anisotropy and etching rate etc.The electrical discharge power is kept high and the energy of thecharged particles is also kept high to obtain high etch rate and goodetching anisotropy in small dimensional structures. The passivation andetching sequence can be, but may not need to be, reiterated and adjusteduntil the completion of the etching task.

To facilitate understanding, FIG. 3 is a flow chart of an embodiment ofthe invention. A photoresist mask is provided on a layer to be etched(step 304). FIGS. 4A-F are schematic illustrations of the process. FIG.4A shows a photoresist mask 404, which has been provided on an oxidelayer 408 to be etched, which is on a substrate. The substrate is placedin a process chamber (step 306).

FIG. 5 is a schematic view of a process chamber 500 that may be used inthe preferred embodiment of the invention. In this embodiment, theplasma processing chamber 500 comprises confinement rings 502, an upperelectrode 504, a lower electrode 508, a gas source 510, and an exhaustpump 520. The gas source 510 comprises a passivation gas source 512, anetchant gas source 514, and an additional gas source 516. Within plasmaprocessing chamber 500, the substrate wafer 580, on which the oxidelayer is deposited, is positioned upon the lower electrode 508. Thelower electrode 508 incorporates a suitable substrate chucking mechanism(e.g., electrostatic, mechanical clamping, or the like) for holding thesubstrate wafer 580. The reactor top 528 incorporates the upperelectrode 504 disposed immediately opposite the lower electrode 508. Theupper electrode 504, lower electrode 508, and confinement rings 502define the confined plasma volume 540. Gas is supplied to the confinedplasma volume by gas source 510 through a gas inlet 543 and is exhaustedfrom the confined plasma volume through the confinement rings 502 and anexhaust port by the exhaust pump 520. The exhaust pump 520 forms a gasoutlet for the plasma processing chamber. A first RF source 544 iselectrically connected to the upper electrode 504. A second RF source548 is electrically connected to the lower electrode 508. Chamber walls552 define a plasma enclosure in which the confinement rings 502, theupper electrode 504, and the lower electrode 508 are disposed. Both thefirst RF source 544 and the second RF source 548 may comprise a 27 MHzpower source and a 2 MHz power source. Different combinations ofconnecting RF power to the electrode are possible. A modified Exelan2300 DFC (Dual Frequency Confined) made by LAM Research Corporation™ ofFremont, California may be used in a preferred embodiment of theinvention. A controller 535 is controllably connected to the first RFsource 544, the second RF source 548, the exhaust pump 520, a firstcontrol valve 537 connected to the deposition gas source 512, a secondcontrol valve 539 connected to the etch gas source 514, and a thirdcontrol valve 541 connected to the additional gas source 516. The gasinlet 543 provides gas from the gas sources 512, 514, 516 into theplasma processing enclosure. A showerhead may be connected to the gasinlet 543. The gas inlet 543 may be a single inlet for each gas sourceor a different inlet for each gas source or a plurality of inlets foreach gas source or other possible combinations.

A protective layer 412 is formed on the photoresist mask 404, as shownin FIG. 4B (step 308). It is preferred that the deposition be asymmetricso that the amount of deposition is formed preferentially more on themasking material. It is preferred such a process is aided by theline-of-sight of the location to the deposition source as well as by theselective nature of the chosen CVD process. In other words, thedeposition chemistry be chosen in such a way that a coating is formedpreferentially on the masking materials due to differences in thechemical inertness of the materials. As can be seen in FIG. 4B a thickerprotective layer 412 is formed on the top of the photoresist mask 404than on the oxide surface on the bottom of the photoresist mask and onthe sidewalls of the photoresist mask. In the preferred embodiment, thedeposition is done in-situ in an etch chamber using a chemical vapordeposition (CVD) process, which also deposits a thin protective layer onthe sidewall of the photoresist. Preferably the deposition uses some ionenergy to allow for selectivity of such deposition.

In other embodiments, the processing conditions may be changed to varythe thickness and spatial distribution of the protective layer. Forexample, it may be desirable to form a thicker coating on the sidewallof the etching structures as the etching proceeds deeper in order toprotect the etching structure from further distortion by the subsequentetching. A variation of processing conditions may provide for this.Since passivation and etching are separate steps, the process conditionsfor passivation may be optimized for this result without interferingwith the etching process.

During the deposition, the fluorine-to-carbon ratio of the depositiongas is not greater than 2:1. Examples of deposition chemistries that maybe used for CVD may be, but are not limited to, CH₃F, CH₂F₂, C₂H₅F,C₃H₇F, C₂H₃F, CH₄, C₂H₄, C₂H₆, C₂H₂, C₃H₈, and SiH₄, Si(CH₃)₄,Si(C₂H₅)₄. It is preferred that these chemicals are halogen free or havea halogen to carbon ratio of no greater than 2:1. Without being limitedby theory, it is believed that the carbon based chemistry forms a thinetch resistant amorphous carbon layer. The silane SiH₄ would be used toform an amorphous silicon layer (or polyamorphous silicon) over thephotoresist. In addition, the protective layer may have been modifiedwith the presence of some F and H components. The presence of otherelements, such as F, may be used to yield selective activity ondifferent material surfaces such that deposition occurs preferentiallyon one but not the other materials, such as on the photoresist maskmaterials but not on SiO₂ layer, under appropriate ion bombardment. Thethinness and etch resistance provides a protection sufficient to resistphotoresist etch or damage and thin enough to allow etching of thedesired feature shape. Other methods, such as sputtering, may be used todeposit a protective layer on the photoresist mask before etching. Thepassivation step is an independent step in the etch process which mayinclude different combinations of deposition gases for different etchingapplications of different materials, where the deposition provides aprotective coating around the etching features including the maskingfeatures using possible multistep gas switching sequences. To accomplishthis step, the controller 535 may cause the first valve 537 to allow adeposition gas from the deposition gas source 512 into the processchamber 500, while causing the second valve 539 from preventing etchinggas from the etchant gas source 514 from entering the process chamber.The controller 535 may also control the power supplied by the first andsecond RF sources 544, 548 and the exhaust pump 520. The controller mayalso be used to control the wafer pressure, backside He coolingpressure, the bias on the substrate, and various temperatures.

Table I is a table of some of the parameters that may be used in apassivation and etching step in the preferred embodiment of theinvention.

TABLE I Preferred More Preferred Most Preferred Range Range Range BiasVoltage >50 volts >100 volts >300 volts Bias Energy >50 eV >100 eV >300eV

The bias may be provided by placing a constant voltage between an upperelectrode above the substrate and a lower electrode below the substrate.In the preferred embodiment, an electrical negativity can be formed onthe substrate holding the wafer materials (thereby applying a bias tothe wafer) by applying a radio frequency (RF) voltage supplied by an RFpower generator. This has the effect of drawing the positively chargedparticles towards the electrically biased substrate at an energydetermined by the electrical negativity controlled by the amplitude ofthe RF voltage. It is, therefore, possible to supply and vary the ionbombardment energy by controlling the RF power (and hence the RFvoltage) applied to the substrate holder.

Next, the oxide layer 408 is etched through the photoresist mask 404, toform the trench 416, as shown in FIG. 4C. Etching applications mayinclude, but are not limited to, a dielectric contact etch (high aspectratio contact (HARC) or damascene), conductor trench etch (shallow ordeep), self-aligned contact etch, gate mask open etch, contact etch, viadielectric etch, dual-damascene via etch, dual damascene trench etch,conductor gate etch, conductor deep trench etch, conductor shallowtrench isolation etch, and hardmask opening. Preferably, the etch uses ahigh ion energy to provide a directional etch. The etch may remove someof the protective layer 412, as shown. All of the protective layer onsome of the surfaces may be removed. In this example, the protectivelayer forming the side wall on the photoresist 404 has been removed.Other parts of the protective layer may only be partially removed. Inthis example, only part of the protective layer 412 on the top surfaceof the photoresist 404 has been removed. In other embodiments, otherparts of the protective layer may be partially etched way or completelyetched away. To accomplish this step, the controller 535 may cause thefirst valve 537 to stop the flow of the deposition gas from thedeposition gas source 512 into the process chamber 500, while causingthe second valve 539 to allow the etching gas from the etchant gassource 514 to flow into the process chamber. The controller 535 maychange the power supplied by the first and second RF sources 544, 548and change the setting of the exhaust pump 520 to accommodate theetching. The controller may also be used to change the wafer pressure,backside pressure, and various temperatures to accommodate the etchingprocess. Since this etch step uses high energy ions to provide adirectional etch, a polymer former gas is provided during the etch. Thepolymer former gases may be, for example, hydrocarbons, fluorocarbons,and hydrofluorocarbons, such as C₄F₆, C₄F₈, CH₃F, CH₂F₂, CH₄, C₃F₆,C₃F₈, and CHF₃. These polymer former gases would form a polymer layerthat is constantly added and etched away during the etch.

Table II is a table of some of the parameters that may be used in anetching process in the preferred embodiment of the invention.

TABLE II Preferred More Preferred Most Preferred Range Range Range BiasVoltage >200 volts >300 volts >400 volts Bias Energy >200 eV >300eV >400 eV

After the contact hole is at least partially etched, a determination ismade on whether to etch more (step 316). This may be done by a setrecipe or by taking a measurement. If more etching is desired, then theprocess cycles back to step 308, where an additional protective layer418 is deposited on the photoresist mask, as shown in FIG. 4D. In thisexample, the remaining part of the old protective layer becomes part ofthe new protective layer 418. In this step, again the controller 535opens the first control valve 537 to provide deposition gas and closesthe second control valve 539 to stop the flow of the etching gas. Thecontroller 535 may also change other parameters to accommodate thedeposition.

The contact hole is then further etched through the photoresist mask(step 312), providing a deeper contact hole 416, as shown in FIG. 4E. Inthis step, again the controller 535 closes the first control valve 537to stop the deposition gas and opens the second control valve 539 toallow the flow of the etching gas. The controller 535 may also changeother parameters to accommodate the etching.

Preferably, this cycle or loop of providing alternating deposition andetching steps is repeated more than once. Preferably, this cycle isrepeated more than three times. Preferably, this cycle is repeated atleast five times. This cycle may be repeated dozens of times. It may bedesirable to repeat this cycle 100 times.

Preferably, in at least the last cycle, the etching step completelyetches away the protective layer, as shown in FIG. 4E. When no furtheretching is desired, the photoresist mask is stripped (step 320) to yieldthe oxide layer 408 with a contact hole 416, as shown in FIG. 4F. Thephotoresist mask may be stripped in the process chamber 500 or afterremoval from the process chamber 500.

In other embodiments, an etch step may be added before step 308 fordepositing a protective layer on the photoresist mask.

Preferably, the etching and the deposition of the protective layer aredone in the same chamber, but may be done in different chambers. AnExelan, DFC 2300 made by LAM Research Corp. of Fremont, Calif. may beadapted to perform both the deposition and etch steps. Since thedeposition and etch are done in the same chamber, cycling between thedeposition and etch may be done quickly. Examples of materials for thephotoresist mask may include, but are not limited to the newergeneration of photoresist, such as, deep UV photoresist, 193 nmphotoresist, 157 nm photoresist, EUV photoresist, e-beam photoresist,and x-ray photoresist. The older generation of photoresist polymermaterials are designed to contained unsaturated C—C bonds, such as theC—C double bond and even C—C triple bonds to provide the required highetching resistance, namely, chemical inertness to the etching gasmixture. These bonds are strong and require a high activation energy tobreak and therefore, at relatively low ion energies, the oldergeneration photoresist can show remarkably low etching rate to theetching gas mixture. The newer generation of photoresist, including 193nm and 157 nm, does not contain these unsaturated bonds because theseunsaturated bonds absorbs at the lithography exposure wavelength,leading to much reduced photoresist etching resistance. By providing aprotective coating on the photoresist during the etching phase, using anetching mixture containing at least one passivation gas, the etchingresistance of the photoresist is much improved, even at high ionbombardment energy. The high ion bombardment energies at which theinvention may improve etching resistance of the photo resist may be50-2,000 eV. More preferably the ion bombardment energy may be 200-1,500eV. Most preferably the ion bombardment energy is 500-1,000 eV.

EXAMPLE

A specific example of the invention, for etching a SiO₂ layer with a 193photoresist mask and a bottom antireflective coating (BARC) between theSiO₂ layer and the photoresist mask, uses an Exelan DFC 2300 for theprocess chamber 500. In the process chamber 500, a BARC etch isperformed. The BARC etch has a pressure of 110 millitorr, which may beset by the confinement rings 502, the exhaust pump 520 and the flow ratethrough the gas inlet 543. The power applied at 27 MHz is 1200 watts,and no power at 2 MHz through the electrodes 504, 508. The etchchemistry is 700 sccm of Argon, 60 sccm of CF₄, and 12 sccm of O₂. Theupper electrode 504 is placed at a temperature of 180° C. The chuckformed by the lower electrode 508 is placed at a temperature of 10° C. Abackside inner zone chuck pressure of helium is placed at 15 torr. Abackside outer zone chuck pressure is placed at 15 torr. In thisexample, the BARC etch is maintained for 50 seconds. The controller 535controls these parameters. The additional gas source 516 may be used toprovide gases for the BARC etch. The additional gas source 516 mayrepresent more than one gas source. The third valve 541 may representmore than one valve, so that the additional gases may be independentlycontrolled by the controller 535. For an Exelan DFC 2300, a back sidepressure of helium is used to cool the chuck. The Exelan DFC 2300 allowsfor an inner backside pressure, which is closer to the center of thechuck and an outer backside pressure which is closer to the outer edgeof the chuck. The controller 535 is able to control these pressures.

A deposition of the protective layer is performed in the Exelan DFC 2300at a pressure of 50 millitorr, with 800 watts applied at 27 MHz and 400watts applied at 2 MHz. The deposition chemistry is 500 sccm of Argonand 50 sccm of CH₃F. The upper electrode is placed at a temperature of180° C. The chuck is placed at a temperature of 10° C. The backsideinner zone chuck pressure of helium is placed at 30 torr. The backsideouter zone chuck pressure is placed at 12 torr. In this example, thedeposition gas source 512 would provide the CH₃F, which is not providedduring the etching. The argon may be provided from the additional gassource 516, since argon is provided during both the deposition andetching. The controller 535 would open the first valve 537 and close thesecond valve 539. The controller would also control the flow of argonfrom the additional gas source. The controller 535 would control thepower and other parameters as specified above.

An etching of the SiO₂ layer is performed in the Exelan DFC 2300 at apressure of 40 millitorr, with 2500 watts applied at 27 MHz and 3500watts applied at 2 MHz. The etch chemistry is 400 sccm of Argon, 36 sccmof C₄F₆, and 30 sccm of O₂. The C₄F₆ would be a polymer former gas,which provides polymerization during the etching. The O₂ would be theetching enabler gas. Although the fluorine from C₄F₆ is used in etching,the fluorine in this example requires the presence of oxygen to enableetching. The upper electrode is placed at a temperature of 180° C. Achuck is placed at a temperature of 10° C. A backside inner zone chuckpressure of helium is placed at 30 torr. A backside outer zone chuckpressure is placed at 12 torr. In this example, the etchant gas source514 would provide the C₄F₆ and O₂, which is not provided during thedeposition, although C₄F₆ without oxygen may be used during depositionThe controller 535 would close the first valve 537 and open the secondvalve 539. The controller would also control the flow of argon from theadditional gas source. The controller 535 would control the power andother parameters as specified above.

In this example, first the BARC etch is performed for 50 seconds. Next,the deposition of the protective layer (step 308) is performed for 10seconds. Next, the contact hole is etched for 25 seconds (step 312).Then the deposition of the protective layer is performed for 10 seconds(step 308). The etch of the trench for 25 seconds (step 312) and thedeposition of the protective layer for 10 seconds (step 308) is repeatedfour times. A final etch of the trench is performed for 80 seconds (step312). The cycle is completed (step 316) and the photoresist is stripped(step 320). Therefore, in this example, the deposition (step 308) andetch (step 312) cycle is performed for 5 cycles.

Another notation for this same sequence can be written as:

50 sec. BARC etch+10 sec. deposition+4×(25 sec. etch+10 sec.deposition)+80 sec. etch.

In this example, the protective layer is preferentially formed on themask and sidewalls of the feature, so that the protective layer isthicker on the mask and sidewalls of the feature than on the bottom ofthe feature or that no protective layer is formed at all at the bottomof the feature.

Different conditions may be used between cycles to more specificallytailor the conditions to the process. Additional processes may be addedto each cycle. Although in this example the process chamber is an ExelanDFC 2300, other modified etching systems may be used. FIG. 6 is aphotomicrograph of a SiO₂ layer 604, which was masked with a 193photoresist mask to form high aspect ratio contact (HARC) etches 608,using the inventive deposition of a protective layer and etch process.FIG. 7 is a photomicrograph of a SiO₂ layer 704, which was masked with a193 photoresist mask to form high aspect ratio contact (HARC) etches708, without using the inventive deposition of a protective layer andetch process. As can be seen by comparing FIG. 6 and FIG. 7, theinventive process of deposition and etching provides the desired patterntransfer from the photoresist mask (the original mask patterns arearrays of circular holes) in that the contacts are more circular. On theother hand, the prior art method of an etch without the deposition of aprotective layer for the photoresist causes a distortion of the originalpatterns, which is apparent in the dielectric layer as shown by the moreirregular shape of the contact holes and which is not acceptable. Theprotective layer on the sidewalls of the photoresist and trench may alsoprevent striation, that is found in some etch processes.

The invention provides a more cost effective process than the use of astacked mask, since the production of a stacked photoresist mask is morecomplicated. The invention may also provide better etch results at lessexpense than a stacked mask process.

The layer to be etched may be a dielectric layer (such as siliconoxide), a conductive layer (such as metal and silicon or other type ofsemiconductors), or a hardmask layer (such as silicon nitride andsilicon oxynitride). For etching a conductor layer, halogens, such aschlorine, fluorine, or bromine, may be used in the etching step, wherethe deposition may contain chemicals used to deposit a C-rich thin filmor a thin film containing Si.

In the preferred embodiment of the invention, it is desirable that someof the components of the deposition gas are not mixed with components ofthe etch gas, since some mixing decreases the efficiency of having aseparate deposition and etch process. As a result, the controller shouldtime the gas flows so that one gas is depleted before another gas isadded.

In the preferred embodiment, the etchant gas from the etching gas sourceis not provided to the plasma processing chamber during the depositionstep and the deposition gas from the deposition gas source is notprovided to the plasma processing chamber during the etching step. Thismay be done by not providing a component of the etching gas ordeposition gas. For example, oxygen or an oxygen containing gas is a keyetching component to an etching gas. Even though C₄F₆ is also used inthe etchant gas, etching cannot be accomplished by C₄F₆ without oxygenin this example. So by not providing oxygen or an oxygen containing gasduring the deposition step is a method of not providing the etching gasduring the deposition step, even if C₄F₆ is provided during deposition.It is also preferred that the deposition process is a non-etching ornegligently etching at most (comprising less than 10% of the layer to beetched) for forming the protective coating. Such a deposition processmay be, but is not limited to, CVD deposition or sputtering, since CVDand sputtering are not used for etching. If the deposition gas is thesame as the polymer former in the etch step, then the deposition gas maybe provided during the etch step. In such a case, one difference betweenthe deposition step and the etch step is that an etching component ofthe etch gas is present only during the etch step. In addition, biaspower during the etch step may be higher to provide the directionaletching.

Providing a separate deposition step and the presence of the polymerformer to provide polymerization during the etch step allows the use ofhigher energy etching ions for higher etching rate and betteranisotropic etching..

By keeping passivation gases in an etching mixture, it is possible touse higher ion energies without unacceptable erosion and damage of theetching mask. Additionally, anisotropic etching can be achieved duringthe duration of the etching step. By using separate passivation steps,profile and mask protection can be optimized by choosing, for example, apassivation chemical mixture that forms a harder and more durablecoating than produced by an etching mixture, since the inter-reaction ofetching and retardation gases in the discharge can degrade the qualityof the coating. Additionally, the passivation chemistry conditions, suchas pressure and concentration, may be tailored to optimize theproperties of the passivation coating such as the composition,thickness.

Therefore, by having independent passivation and etch-passivation stepsprocessing conditions, such as temperature, power, pressure, ion energy,and processing gases, may be independently controlled varied to provideoptimal conditions for each step to provide an optimized coating and anoptimized etch.

Other inert gases instead of argon may be used as carrier gases duringboth the etching and deposition. An example of another inert gas wouldbe neon.

In an embodiment of the invention, the chamber wall areas, which maycontact the plasma (a mixture of chemicals and charged particlessustained by the electrical discharge), are made to be as small aspossible and to be maintained at elevated temperatures. The object ofthis is to minimize the total deposition on the chamber wall areas so asto avoid the so-called “memory” effect, by which the chemical elementscontained in the coating of the chamber wall areas formed in oneprocessing step can be released to interfere with the subsequent steps.

It may also be desirable that the gas travel time from the precursorsource to the processing chamber is made to be very short. The gas flowstability time, denoting the time to establish a constant desired flowand the time to establish complete absence of the said gas at theprocessing chamber, is made to be very short so that the transition fromone stable gas mixture composition to the next can be made to be veryfast. The object of this is to avoid inter-mixing of chemicals betweentwo different steps, which can degrade the performance.

It may also be desirable that the electrical system and the controlnetwork controlling the conversion of the electrical power into anelectrical discharge reacts very fast with respect to the changes of thedischarge conditions and power requirements. Furthermore, it maydesirable to be able to quickly change and stabilize other t externalconditions of the processing chamber, such as the pressure of the gasmixture and the temperature of the wafer substrate. Since the twodifferent steps may be repeated a large number of times processconditions to accommodate each step must be change several times.Allowing such process conditions to be changed quickly allows for afaster cycling time and allows the process conditions to be variedsignificantly between steps to optimize each step individually.Therefore, it may also be desirable to have a central computerizedsystem that is able to control and synchronize the rapid changing of theprocessing conditions. The computer is used to send commands for therequired changes and synchronize with a predetermined time delays ofvarious devices providing the plurality of condition changes in theprocessing chamber.

The deposition step may comprise a series of different coating steps.The etching step may comprise a series of different etching steps.

FIGS. 8A and 8B illustrate a computer system 800, which is suitable forusing as the controller 535. FIG. 8A shows one possible physical form ofa computer system that may be used for the controller 535. Of course,the computer system may have many physical forms ranging from anintegrated circuit, a printed circuit board, and a small handheld deviceup to a huge super computer. Computer system 800 includes a monitor 802,a display 804, a housing 806, a disk drive 808, a keyboard 810, and amouse 812. Disk 814 is a computer-readable medium used to transfer datato and from computer system 800.

FIG. 8B is an example of a block diagram for computer system 800.Attached to system bus 820 are a wide variety of subsystems.Processor(s) 822 (also referred to as central processing units, or CPUs)are coupled to storage devices, including memory 824. Memory 824includes random access memory (RAM) and read-only memory (ROM). As iswell known in the art, ROM acts to transfer data and instructionsuni-directionally to the CPU and RAM is used typically to transfer dataand instructions in a bi-directional manner. Both of these types ofmemories may include any suitable type of the computer-readable mediadescribed below. A fixed disk 826 is also coupled bi-directionally toCPU 822; it provides additional data storage capacity and may alsoinclude any of the computer-readable media described below. Fixed disk826 may be used to store programs, data, and the like and is typically asecondary storage medium (such as a hard disk) that is slower thanprimary storage. It will be appreciated that the information retainedwithin fixed disk 826 may, in appropriate cases, be incorporated instandard fashion as virtual memory in memory 824. Removable disk 814 maytake the form of any of the computer-readable media described below.

CPU 822 may be also coupled to a variety of input/output devices, suchas display 804, keyboard 810, mouse 812 and speakers 830. In general, aninput/output device may be any of: video displays, track balls, mice,keyboards, microphones, touch-sensitive displays, transducer cardreaders, magnetic or paper tape readers, tablets, styluses, voice orhandwriting recognizers, biometrics readers, or other computers. CPU 822optionally may be coupled to another computer or telecommunicationsnetwork using network interface 840. With such a network interface, itis contemplated that the CPU might receive information from the network,or might output information to the network in the course of performingthe above-described method steps. Furthermore, method embodiments of thepresent invention may execute solely upon CPU 822 or may execute over anetwork such as the Internet in conjunction with a remote CPU thatshares a portion of the processing.

In addition, embodiments of the present invention further relate tocomputer storage products with a computer-readable medium that havecomputer code thereon for performing various computer-implementedoperations. The media and computer code may be those specially designedand constructed for the purposes of the present invention, or they maybe of the kind well known and available to those having skill in thecomputer software arts. Examples of computer-readable media include, butare not limited to: magnetic media such as hard disks, floppy disks, andmagnetic tape; optical media such as CD-ROMs and holographic devices;magneto-optical media such as floptical disks; and hardware devices thatare specially configured to store and execute program code, such asapplication-specific integrated circuits (ASICs), programmable logicdevices (PLDs) and ROM and RAM devices. Examples of computer codeinclude machine code, such as produced by a compiler, and filescontaining higher level code that are executed by a computer using aninterpreter. Computer readable media may also be computer codetransmitted by a computer data signal embodied in a carrier wave andrepresenting a sequence of instructions that are executable by aprocessor.

While this invention has been described in terms of several preferredembodiments, there are alterations, permutations, and substituteequivalents, which fall within the scope of this invention. It shouldalso be noted that there are many alternative ways of implementing themethods and apparatuses of the present invention. It is thereforeintended that the following appended claims be interpreted as includingall such alterations, permutations, and substitute equivalents as fallwithin the true spirit and scope of the present invention.

What is claimed is:
 1. A method for etching a feature in a layer throughan etching mask comprising: forming a protective coating on exposedsurfaces of the etching mask and vertical sidewalls of the feature witha passivation gas mixture; and etching the feature through the etchingmask with reactive etching mixtures containing at least one etchingchemical and at least one passivation chemical, wherein the forming theprotective coating provides no protective coating on a bottom of thefeature.
 2. The method, as recited in claim 1, wherein the etchingcomprises providing an ion bombardment energy of greater than 200electron volts to the substrate.
 3. The method, as recited in claim 2,wherein the etching chemical contains a polymer former and an etchenabler.
 4. The method, as recited in claim 3, wherein the passivationand etching are performed in a common plasma processing chamber.
 5. Themethod, as recited in claim 4, wherein the deposition uses anon-directional deposition and the etching step uses a directionaletching.
 6. The method, as recited in claim 5, wherein the passivationis a non-etching or a negligibly etching deposition.
 7. The method, asrecited in claim 6, wherein the deposition process is selected from atleast one of chemical vapor deposition and sputtering.
 8. The method, asrecited in claim 7, wherein the layer is only a single layer, whereinthe feature is etched only in the single layer during the forming theprotective coating and etching the feature, wherein the forming theprotective layer and etching are performed in a sequentially alternatingfashion at least four times, to etch only the single layer.
 9. Themethod, as recited in claim 1, wherein the etching mask is a photoresistmask 193 nm or below generation.
 10. The method, as recited in claim 1,wherein at least one passivation chemical releases a polymerizing agentthat is more chemically active to the layer than the mask materials. 11.The method, as recited in claim 10, wherein at least one passivationchemical is a hydrofluorocarbon with F:C ratio of less than 2:1.
 12. Themethod, as recited in claim 10, wherein at least one of the passivationchemical is one of the CH₃F, CH₂F₂, C₂H₅F, C₂H₄F₂, C₃H₇F, C₃H₆F₂, C₂H₃F,CH₄, C₂H₆, C₂H₄, C₃H₈, C₂H₂.
 13. The method, as recited in claim 10,wherein the at least one passivation chemical is a mixture of Ar andCH₃F.
 14. The method, as recited in claim 10, wherein the ion energyprovided in the passivation step is greater than 100 electron volts. 15.The method, as recited in claim 1, wherein the layer is only a singlelayer, wherein the feature is etched only in the single layer during theforming the protective coating and etching the feature.
 16. The method,as recited in claim 1, wherein forming the protective coating isaccomplished using a selective chemical vapor deposition, which formsthe protective coating on exposed surfaces of the etch mask and verticalsidewalls of the feature, but not on the bottom of the feature.
 17. Themethod, as recited in claim 1, wherein the etch mask is a photoresistmask, and wherein the forming a protective coating forms a protectivecoating that is more etch resistant than the etch mask.
 18. The method,as recited in claim 17, wherein the forming the protective coating formsa protective coating of amorphous carbon.
 19. The method, as recited inclaim 17, wherein the forming the protective coating forms a protectivecoating of polyamorphous silicon.
 20. The method, as recited in claim17, wherein the forming the protective coating forms a pseudo hardmask.